The overall goal of this application is to determine the short-term efficacy of N-carbamyl-L-glutamate (NCG) for the treatment of five inborn errors of metabolism that cause hyperammonemia and consequent brain damage: N-acetylglutamate synthase (NAGS) deficiency, carbamyl phosphate synthetase I (CPSI) deficiency, propionic acidemia (PA), methylmalonic acidemia (MMA), as well as hyperinsulinism and hyperammonemia syndrome (HHS). Specific Aim 1 is to determine whether a three-day treatment with NCG improves or restores ureagenesis in patients with NAGS deficiency, CPSI deficiency, PA, MMA, and HHS as evidenced by 13C incorporation into urea, concentrations of plasma ammonia, urea, and amino acids as well as brain glutamine concentrations measured by magnetic resonance spectroscopy. The results in patients with each of the five inherited disorders will be compared to those obtained in healthy adult volunteers (normal controls). In addition, the results of patients with NAGS deficiency, who the investigators expect to respond best to NCG (positive controls), will be compared to the results from the other four disorders to gauge their degree of correction of ureagenesis in response to NCG. Specific Aim 2 is to evaluate the safety of short-term (three-day) treatment with NCG in the healthy volunteers and patients. Clinical and laboratory safety parameters will be evaluated in all participants, including idiosyncratic symptoms and changes in blood counts as well as liver and kidney functions. The investigators'hypothesis is that NCG will ameliorate deficient ureagenesis in these congenital disorders. Thus, this application will provide important efficacy data for a novel treatment of several rare congenital disorders that are associated with hyperammonemia that often is refractory. Successful conclusion of the study may also afford a rationale for the investigation of other diseases and conditions that are complicated by hyperammonemia, including liver failure of diverse etiology and treatment with valproic acid.